package Question2_7;
import CtCILibrary.LinkedListNode;
public class Question {
public class Result {
public LinkedListNode node;
public boolean result;
public Result(LinkedListNode n, boolean res) {
node = n;
result = res;
}
}
public Question.Result isPalindromeRecurse(LinkedListNode head, int length) {
if (head == null || length == 0) {
return new Question.Result(null, true);
} else if (length == 1) {
return new Question.Result(head.next, true);
} else if (length == 2) {
return new Question.Result(head.next.next, head.data == head.next.data);
}
Question.Result res = isPalindromeRecurse(head.next, length - 2);
if (!res.result || res.node == null) {
return res; // Only "result" member is actually used in the call stack.
} else {
res.result = head.data == res.node.data;
res.node = res.node.next;
return res;
}
}
public boolean isPalindrome(LinkedListNode head) {
int size = 0;
LinkedListNode n = head;
while (n != null) {
size++;
n = n.next;
}
Result p = isPalindromeRecurse(head, size);
return p.result;
}
public static void main(String[] args) {
int length = 10;
LinkedListNode[] nodes = new LinkedListNode[length];
for (int i = 0; i < length; i++) {
nodes[i] = new LinkedListNode(i >= length / 2 ? length - i - 1 : i, null, null);
}
for (int i = 0; i < length; i++) {
if (i < length - 1) {
nodes[i].setNext(nodes[i + 1]);
}
if (i > 0) {
nodes[i].setPrevious(nodes[i - 1]);
}
}
// nodes[length - 2].data = 9; // Uncomment to ruin palindrome
LinkedListNode head = nodes[0];
System.out.println(head.printForward());
Question q = new Question();
System.out.println(q.isPalindrome(head));
}
}